1. Field of the Invention
The invention relates generally to optical scanners, and particularly although not exclusively to scanners for reading bar code symbols. The invention further relates, in its various aspects, to a hand-held scanner of modified spherical or ovoid shape, and to a system for linking a wireless scanner to a particular scanner cradle.
2. Description of Related Art
Various optical readers and optical scanning systems have been developed heretofore for reading indicia such as bar code symbols appearing on a label or on the surface of an article. The bar code symbol itself is a coded pattern of indicia comprised of a series of bars of various widths spaced apart from one another to bound spaces of various widths, the bars and spaces having different light reflecting characteristics. The readers in scanning systems electro-optically transform the graphic indicia into electrical signals, which are decoded into alphanumeric characters that are intended to be descriptive of the article or some characteristic thereof. Such characteristics are typically represented in digital form and untilized as an input to a data processing system for applications in point-of-sale processing, inventory control and the like. Scanning systems of this general type have been disclosed for example, in U.S. Pat. Nos. 4,251,798; 4,369,361; 4,387,297; 4,409,470; 4,760,428; 4,896,026; 5,015,833; 5,262,627; and 5,504,316 all of which have been assigned to the same assignee as the instant application and each of which are hereby incorporated by reference. As disclosed in some of the above patents, one embodiment of such a scanning system resides, inter alia, in a hand held, portable laser scanning device supported by a user, which is configured to allow the user to aim the scanning head of the device, and more particularly, a light beam, at a targeted symbol to be read.
The light source in a laser scanner bar code reader is typically a semiconductor laser. The use of semiconductor devices as the light source is especially desirable because of their small size, low cost and low voltage requirements. The laser beam is optically modified, typically by an optical assembly, to form a beam spot of a certain size at the target distance. It is preferred that the cross section of the beam spot of the target distance be approximately the same as the minimum width between regions of different light reflectivity, i.e., the bars and spaces of the symbol. At least one bar code reader has been proposed with two light sources to produce two light beams of different frequency.
The laser beam may be moved by optical or opto-mechanical means to produce a scanning light beam U.S. Pat. No. 5,144,120 to Krichever et al. employs laser, optical and sensor components mounted on a drive for repetitive reciprocating motion either about an axis or in plane to effect scanning.
Another type of bar code scanner employs electronic means for causing the light beam to scan a bar code symbol, rather than using a mechanical activation. A linear array of light sources activated one at a time in a regular sequence may be imaged upon the bar code symbol to simulate a scanned beam. Instead of a single linear array of light sources, a multiple-line array may be employed, producing multiple scan lines. Such type of scanner is disclosed in U.S. Pat. No. 5,258,605 to Metlitzky et al.
Typically, the semiconductor lasers used in such bar code scanners is an edge-emitting injection laser in which the laser beam is emitted from the p-n junction region on a polished end face of the device. By their physical nature, these known edge-emitting injection lasers emit a beam from a thin region at the p-n junction. A laser beam emanating from a thin source has a large beam divergence which makes focusing difficult and results in a wide range of variability in performance from laser to laser.
A more recently developed form of semiconductor laser is the vertical-cavity surface-emitting laser diode (VCSEL), such as described in "Efficient Room-Temperature Continuous-Wave AlGaInP/AlGaAs Visible (670 nm) Vertical-Cavity Surface Emitting Laser Diodes" by R P Schneider et al. published in IEEE Photonics Technology Letters, Vol. 6, No. 3, March 1994. Reference is also made to U.S. Pat. Nos. 5,283,447; 5,285,455; 5,266,794; 5,319,496; and 5,326,386, which are hereby incorporated by reference, for background information.
The VCSEL has a substantial surface area from which the laser beam is emitted; this area may be patterned. Thus, the beam produced is less divergent in one dimension than with known edge-emitting type semiconductor laser diodes. The output beam is round, and is virtually not astigmatic. Furthermore, VCSELs typically operate at significantly lower currents than edge-emitting laser diodes. Therefore, it also generates less heat.
In the laser beam scanning system known in the art, a single laser light beam is directed by a lens or other optical components along the light path toward a target that includes a bar code symbol on the surface. The moving-beam scanner operates by repetitively scanning the light beam in a line or series of lines across the symbol by means of motion or a scanning component, such as the light source itself or a mirror disposed in the path of the light beam. The scanning component may either sweep the beam spot across the symbol and trace a scan line across the pattern of the symbol, or scan the field of view of the scanner, or do both.
Bar code reading systems also include a sensor or photodetector which detects light reflected or scattered from the symbol. The photodetector or sensor is positioned in the scanner in an optical path so that it has a field of view which ensures the capture of a portion of the light which is reflected or scattered off the symbol, detected, and converted into an electrical signal.
In retroreflective light collection, a single optical component e.g., a rotating mirror, such as described in Krichever et al. U.S. Pat. No. 4,816,661 or Shepard et al. U.S. Pat. No. 4,409,470, both herein incorporated by reference, scans the beam across a target surface and directs the collected light to a detector. The rotating mirror usually is relatively large to receive the incoming light, and only a small detector is required since the rotating mirror can focus the light on to a small field of view, which increases signal-to-noise ratio.
In non-retroreflective light collection, the reflected laser light is not collected by the same optical component used for scanning. Instead, the detector is independent of the scanning beam, and is typically constructed to have a large field of view so that the reflected laser light traces across the surface of the detector. Because the scanning optical component, such as a rotating mirror, need only handle the outgoing light beam, it can be made much smaller. On the other hand, the detector must be relatively large in order to receive the incoming light beam from all locations in the scanned field.
Electronic circuitry and software decode the electrical signal into a digital representation of the data represented by the symbol that has been scanned. For example, the analog electrical signal generated by the photodetector is converted by a digitizer into a pulse or modulated digitized signal, with the widths corresponding to the physical widths of the bars and spaces. Such a digitized signal is then decoded, based on the specific symbology used by the symbol, into a binary representation of the data encoded in the symbol, and subsequently to the alpha numeric characters so represented.
The bar code symbols are formed from bars or elements typically rectangular in shape with a variety of possible widths. The specific arrangement of elements defines the character represented according to a set of rules and definitions specified by the code or "symbology" used. The relative size of the bars and spaces is determined by the type of coding used as is the actual size of the bars and spaces. The number of characters (represented by the bar code symbol) is referred to as the density of the symbol. To encode the desired sequence of the characters, a collection of element arrangements are concatenated together to form the complete bar code symbol, with each character of the message being represented by its own corresponding group of elements. In some symbologies, a unique "start" and "stop" character is used to indicate when the bar code begins and ends. A number of different bar code symbologies exist, these symbologies include UPC/EAN, Code 39, Code 128, Codebar, and Interleaved 2 of 5, etc.
In order to increase the amount of data that can be represented or stored on a given amount of surface area, several new bar code symbologies have recently been developed. One of these new code standards, Code 49, introduces a "two-dimensional" concept by stacking rows of characters vertically instead of extending the bars horizontally. That is, there are several rows of bar and space patterns, instead of only one row. The structure of Code 49 is described in U.S. Pat. No. 4,794,239. Another two-dimensional symbology, known as "PDF417", is described in U.S. Pat. No. 5,304,786.
Still other symbologies have been developed in which the symbol is comprised of a matrix array made up of hexagonal, square, polygonal and/or other geometric shapes. Such symbols are further described in, for example, U.S. Pat. Nos. 5,276,315 and 4,794,239. Such matrix symbols may include Vericode, Datacode, and MAXICODE.
The decoding process of known bar code reading system usually works in the following way. The decode receives the pulse width modulated digitized signal from the digitizer, and an algorithm, implemented in the software, attempts to decode the scan. If the start and stop characters and the characters between them in the scan were decoded successfully and completely, the decoding process terminates and an indicator of a successful read (such as a green light and/or an audible beep) is provided to the user. Otherwise, the decoder receives the next scan, performs another decode attempt on that scan, and so on, until a completely decoded scan is achieved or no more scans are available.
One particular variety of scanner is known as an omni-directional scanner, so called because scanners of this type are capable of reading bar code symbols which are presented to them in any orientation. Typically, an omni-directional scanner may produce a "cross-hatch" type of scan pattern, featuring several sets of parallel lines, each set being angularly spaced from each other set so that the entire 360.degree. is covered. Such cross-hatch patterns are produced by directing a light beam onto a spinning planar or polygonal mirror which scans the beam across a group of stationary mirrors, creating several scan lines. The stationary mirrors are angled with respect to each other, thereby ensuring that the corresponding scan lines are similarly angled.
One particular type of omni-directional scanners known as "presentation" or "projection" scanners is presently available from a number of manufacturers. Typically, these scanners are intended to be used in point-of-sale environments, where items with bar code symbols on them are passed by or presented to the scanner. Examples include the Metrologic MS-700, the Fujitsu Slim Scan 1000, the Spectra Physics Space and the Panasonic ZE-87.
In most point-of-sale environments there is very little room for the scanner, and it is therefore highly desirable for the scanner to be made as small as possible. However, as the scanner is made smaller the scan pattern is made smaller also. This results in a scanner that is not as easy to use, because the operator must be more careful in positioning the bar code symbol to be scanned within the scan pattern. Such positioning must often be done blind, because the scan pattern is normally invisible in normal room lighting, and the scanner is often positioned in any event so that the symbol is not visible to the operator when it is being scanned.
It can clearly be seen, therefore, that it would be desirable to have a scanner which fits into a small package but which creates the largest possible scan pattern. Providing such a scanner is not an easy task, however.
As have been mentioned above, the scan pattern in known scanners is normally generated by a scanning polygonal mirror which scans the laser across a group of stationary mirrors, thereby creating several scan lines. The stationary mirrors are oriented so that the lines reflecting off them converge into the desired scan pattern just outside the exit window of the scanner. Since the size of the scan pattern grows as the distance from the pattern mirrors increases, it will be understood that the further the mirrors are placed behind the exit window the better. However, the further the mirrors are placed behind the window, the deeper the housing has to be to accommodate them.
There is a further design consideration that tends to drive up the thickness or depth of the scanner housing. As stated above, the scan pattern is formed by angling the stationary pattern mirrors so that the lines converge into the desired pattern near to the exit window. The closer the mirrors are to the window, the more steeply the mirrors must be angled to get the lines to converge in the correct place. If the scanner thickness is small, with consequently steeply angled mirrors, the scanning lines will necessarily diverge from the desired pattern rapidly as distance from the window is increased. Accordingly, the pattern decays rapidly farther from the scanner, and the user is thereby forced to bring the bar code symbol up close to the window before recognition will take place.
It will be clear, therefore, that it is thought desirable to have a deep scanner housing so that the mirrors can be placed as far away from the window as possible, so that the pattern will be large at the window, and so that the pattern will remain converged, and useful as a scanning pattern, even as the distance between the window and the bar code symbol increases.
There have been a number of prior art attempts to resolve this conflict between pressure for a deep scanner, to improve performance, and pressure for a narrow scanner, to save space in the checkout area. Some typical prior art solutions are illustrated in FIGS. 9 to 11.
FIG. 9 illustrates a first prior art arrangement in which the scanner housing (or body) 10 is deliberately made narrow, with the distance between a front face 12 and a rear face 14 of the body being only about 1.75 inches (4.4 centimeters). A light beam generated by a laser 16 is shone onto a rotating polygonal mirror 18 which is caused to rotate by a motor 20. The light reflected back from the polygonal mirror 18 impinges upon a plurality of stationary pattern mirrors 22, which direct the light out of the housing 10 via a window 24.
With this arrangement, the stationary mirrors 22 are positioned immediately behind the exit window 24. This results in a slim overall package, but has the disadvantage that the scan pattern does not become good (that is the scan lines do not cross each other) until they have projected a few inches beyond the scanner. This reduces scanner flexibility and performance, because users frequently hold the symbol near to the window. With the arrangement shown in FIG. 9, it is quite possible to move the symbol past the scanner, close to the window, and never to intercept a scan line that is properly oriented to read the presented symbol.
A further prior art arrangement is shown in FIG. 10. In this arrangement the housing 26 is generally smaller than the housing shown in FIG. 9, but is somewhat deeper, with the distance between a front face 42 and a rear face 44 being about 4 inches (10 centimeters). A laser 28 produces a light beam which impinges, in order, on a first fold mirror 30, a second fold mirror 32, a spimintg mirror 34 which is actuated by a motor 36, and a series of stationary pattern mirrors 38. The light is then reflected from the pattern mirrors out of the housing 26 through a window 40.
This arrangement again produces a pattern which is not well formed until about 2.5 inches (6.4 centimeters) from the window, but uses frequently hold symbols closer than this. The small overall size of the housing means that the scan pattern is likewise small, and it is relatively easy for the user to miss the pattern entirely when he brings up a bar code symbol into what he believes to be the correct position.
FIG. 11 shows an improvement on these prior art embodiments. This scanner is contained within a housing 44 which is about 3 inches (7.6 centimeters) in depth between a front surface 46 and a rear surface 48. The length and width dimensions are both about 6.5 inches (16.5 centimeters). A laser 50 produces a light beam which impinges, in order, on a fold mirror 52, a spinning polygonal mirror 54 actuated by a motor 56, and a series of stationary pattern mirrors 57. The light is reflected from these pattern mirrors 57 out of the housing 44 via a window 58.
This arrangement still produces a pattern which is not fully formed at the window. Furthermore, the pattern is of necessity relatively small compared with the overall size of the front face 46 of the housing. In one commercially available embodiment, the window 56 only covers about half of the area of the face 46.
It is another disadvantage for each of the arrangements described above that none is particularly well configured for use when the scanner window is vertical, or nearly vertical, as is becoming popular in warehouse stores and some supermarkets. In such a situation, it is important for the scan pattern to project close to the counter-top, as well as several inches above the counter-top, so that the scan pattern cannot miss a symbol even if it is very close to the counter-top on the side of the package near the scanner. Current scanners, such as those described above, normally have to be partially buried within the counter-top, which of course is expensive. An alternative is to position the scanner on top of the counter-top, but that means that the user may have to lift the item to ensure that the symbol intercepts the scan pattern. That is of course also undesirable, as it produces user fatigue.
Turning now to the embodiments of a system for linking a wireless scanner to a particular scan cradle, it is believed that the closest prior art is represented by U.S. Pat. No. 5,189,291, to Siemiatkowski. U.S. Pat. No. 5,448,046 to Swartz and U.S. Pat. No. 5,151,581 to Kirchever et al are examples of documents showing adjustable stands. All of these patents have been assigned to the present assignee.